Nikolas Cruz, who has been linked to a history of mental illness, is believed to have used a legally obtained AR-15 in the shooting. The attack has led to widespread conversations about links between gun violence and mental illness, and how lawmakers and interest groups are debating potential policy responses.

“Two things typically happen in the wake of a mass shooting. First, politicians claim that mental illness is the major cause of violence in America. Then, advocates for people with mental illness respond by denying there is any relationship whatsoever between mental illness and violence. Both groups are wrong. Research shows that the association between mental illness and violence is not strong, but it does exist.”